a) Conventional Type Heat Exchangers
It is beyond the scope of this patent to attempt to define the various conventional heat exchanger designs currently available in the art. Generally speaking, heat exchangers can be somewhat classified by certain design characteristics. For example, heat exchangers can be finned or unfinned and designed to have large or small pressure drop of the heat transfer fluid flow therethrough. The flow can be classified as either laminar or turbulent or parallel or cross flow. Structurally, the exchanger can be defined as tube type of plate type. Whether or not the heat exchanger is of the plate type or tube type and whether employing fins or unfinned and whether using cross flow (turbulent) or parallel flow (laminar) or large or small pressure drops, inherent in the transfer of heat is a boundary layer between the fluids which heretofore limited the heat transfer coefficient, H.sub.c, in heat exchangers to values in the range of 5-10 btu/(hr. ft.sup.2 .degree.F.).
b) Furnace Art
Within the furnace art, there are applications where heat must be convectively transferred to or from the work at extremely high heat transfer rates. In certain applications, high convective heat transfer rates have been achieved by using free standing gas jets to directly impinge the work. Two examples of jet impingement can be found in my U.S. Pat. No. 4,830,610 and my U.S. Pat. No. 4,693,015. In my '015 patent, heated jets are used for paper drying. In my '610 patent, heated jets are used to impinge a hollow cylindrical shell to effect high heat transfer therewith. In such applications as well as in numerous strip line applications, a gas is pressurized in a conduit which contains precisely machined orifices or alternatively slits which direct a high speed gas jet to impinge the work, generally normal or perpendicular to the work's surface. After impingement, the spent gas from the jet is simply dissipated into space as in a strip line. Alternatively, the spent jet is dispersed within the furnace chamber, as in my prior patents, to some point in the chamber where it is drawn back by a fan, heated, repressurized and pumped back into the conduit for reformation as a jet. Such arrangements require that the orifices or slits be of relatively small sizes precisely controlled in spacing and size to achieve the desired high heat transfer coefficients. In all such furnace applications, once the jet impinges the work, it is spent notwithstanding the fact that the gas from the spent jet still has heat of enthalpy or sensible heat or available heat which is not utilized. Thus, the concept of jet impingement, widely used in the furnace art, has, heretofore, not believed to have found application in the heat exchanger art, at least in the form to be discussed hereafter. That is, while both heat exchanger and furnace applications are obviously concerned with transferring heat, one of the primary concerns in the heat exchanger art is to utilize as much heat from the heat transferring fluid to produce an efficient design while the furnace application is only concerned with transferring heat at a predetermined high rate.
In this connection, it is also known from my previous work with Gas Research Institute to provide a gas fired heating mantle for heating a retort furnace. In the GRI heating mantle, a plurality of vertically spaced annular baffles in fluid communication with one another by "slotted jets" provides a mantle for heating a tubular member, i.e. a retort, connected to the inside diameter of the baffles. Heated products of combustion pass through the angularly offset slotted jets to create turbulent gas flow within each annular chamber thus utilizing the heat in an efficient manner. The turbulent gas flow improves the convective heat transfer to the retort but obviously not at the high convective heat rates achieved in jet impingement.
c) Batch Coil Annealing Furnaces
There are two methods for annealing steel strip which are in conventional use today. The first method which is conventionally accepted as the preferred method for achieving highest metallurgical and physical property control of the strip is to heat the strip as it continuously travels at high speed through looping towers past gas jets and which thereafter is wrapped into coils for shipment to the end user. The second older method of annealing strip is to stack the strip wound into coils vertically on their edges, one on top of the other, within a bell shaped annealing cover. Heated gas is then circulated about the coils within the cover to achieve annealing. Annular spacers are provided between adjacent covers and the spacers are open to permit furnace atmosphere to circulate between the edges of adjacent coils. Further, some spacers, i.e. convector plate spacers, have tabs or baffles which "wipe" the furnace atmosphere against coil edges as the furnace atmosphere passes through the spacer. Such arrangements improve the heat treatment at the edges of the coil. However, it is widely known and conventionally accepted that batch coil annealing does not produce consistent metallurgical strip characteristics, especially at the edges of the strip, which are achieved when the strip is annealed continuously.